One of the most robust findings in health psychology is that poor quality relationships place people at risk for an array of disease outcomes, including inflammation, depression, and premature mortality. Thus, identifying scalable interventions that improve relationship quality, thereby improving disease outcomes, is an essential public health goal. Mindfulness interventions, which encourage attention towards and acceptance of current experiences, are a promising target for improving relationship quality. For example, people who are higher in trait mindfulness also self-report having higher romantic relationship quality. In addition, a mindfulness intervention improved self-reported romantic relationship quality relative to a non-active wait-list control. The wait-list comparison condition from prior work makes it unclear whether the mindfulness intervention itself or non-specific intervention factors (e.g., positive treatment expectancies) were driving positive relationship outcomes, a significant limitation. Thus, a critical next step is to compare a mindfulness intervention to an active control comparison condition. The overarching aim of this proposal is to experimentally test whether a mindfulness intervention improves relationship quality, assessed via both subjective and objective measures, relative to an active control comparison. We focus specifically on mindfulness and romantic relationship quality in this exploratory R21 because this focus builds on a well-established link between romantic relationships and disease outcomes. Romantic couples from the community will be randomly assigned to one of two arms: mindfulness vs. active control. Both interventions will be completed on a smart-phone for 14 days using identical intervention activities as our existing published research. Before and after the 14-day period, couples will attend a lab visit and provide subjective and objective relationship quality data. Before and after the intervention, participants will also provide secondary health data: sleep quality, self-rated health, depressive symptoms, personal well-being, heart rate, systolic blood pressure, and diastolic blood pressure. Although multiple high impact theoretical papers have underscored the need to examine the effect of a mindfulness intervention on relationship quality, empirical work is sparse. This lack of research is surprising given that poor quality relationships robustly increase risk for morbidity and accelerated mortality. This study is the first step towards testing a mindfulness intervention as a means to improving relationship quality. If the aims of this R21 are achieved, the research team will use these data to propose a larger study about mindfulness, relationships, and disease outcomes. The long-term goal of this research program is to understand whether a mindfulness intervention enhances relationship quality, thereby improving disease outcomes. If this goal is achieved, the research team will have identified a scalable intervention for enriching the quality of people?s relationships, with the downstream consequence of also improving their health. In doing so, these data would identify improved relationship quality as a novel mechanism through which mindfulness alters disease outcomes.